Direct and alternating current amplifier



Aug. l2, 1941. F. J. BINGLEY 4DIRECT AND ALTERNATING CURRENT AMPLIFIER Original Filed Nov. 23, 1935 Patented Aug. 12, 1941 UNITED STATES PATENT OFFICE DERECT AND ALTERN-'ATING CURRENT AMPLIFIER Frank J. Bingley, Philadelphia, Pa., assgnor, by

mesne assignments, to Philco Radio and Television Corporation, Philadelphia, Pa., a corporation of Delaware Original application November 23, 1935, Serial No. 51,324. Divided and this application July 5, 1939, Serial No. 282,934

14 Claims.

Consequently, the invention f 1 ticularly where the frequency range to be transwhere the deleterious effect of the capacity to ground inserted by such direct coupling, which would tend to by-pass high frequency components to be transmitted, may be avoided. In

accordance with the invention, the signal to be amplified, which Will include Zero and high frequency components, is supplied to two channels by complementary frequency selective networks so that only the higher frequencies appear in the one channel and only the lower frequencies including Zero frequency components appear in the other channel. Amplifier means are provided in each channel, the one being arranged to transmit the higher frequency components, whereas the other is arranged to transmit the lower frequency components, and then signals from each channel are re-combned.

This application is a division of my copending application Serial No. 51,324, filed November 23, 1935, now U. S. Patent No. 2,171,536, issued September 5, 1939, and the device described herein may be employed in the television system disclosed in said parent application to transmit both the brightness and the contrast signal described therein. The use of the invention is not, however, restricted to television systems.

The invention may be fully understood by reference to the accompanying drawing where- 1n:

v Fig. l is a circuit diagram of a preferred form of the invention in which a multi-stage amplier is illustrated.

Fig. 2 is a circuit diagram of another form of the invention; and

Fig. 3 is an illustration of the method of separating and re-combining the different signalsv of varying frequency.

In a conventional D. C. amplifier, the use of a blocking battery causesv deleterious effects due to the capacitance of the battery to ground. As

as follows:

will be seen from the following description, the present invention enables the use of such a battery without obtaining such deleterious 'effects.

In accordance with this invention, an exactly .compensated equivalent D. C. coupled amplifier,

which has a uniform gain vs. frequency characteristic over the entire video frequency range including zero frequency components and in which there is no phase distortion .as between the input and o-utput signals, may be made by dividing the amplifier stage into two branches: a

conventional A. C. amplier having the usual low frequency cut-off, and an additional D. C. -coupled amplifier having a gain vs. frequency response complementary to the corresponding characteristic of the A. C. amplier. By combining the outputs of the two amplifiers, substantially uniform gain over the entire frequency range is obtained.

Y Such an amplifier is shown in Fig. 1. This amplifier comprises two similar stages as indicated by the dotted line. The signal is applied to the network consisting of resistances R1 and R2 and condensers C1 and C2. The A. C. coupled branch comprises tube V1, coupling condenser C1 and grid leak R1. The conductively coupled stage comprises resistance R2, condenser C2 and battery B1 and the tube V2. The outputs of the two stages are combined in the common anode resistance R3.

The operation of this device is substantially The entire signal will appear across diagonal points X-Y of the network which points connect the network to the signal source and to ground through the battery B2. The portion of the total signal appearing across the resistance R1 is supplied to tube V1, while the portion of the signal appearing across the capacitance C2, is applied to the tube V2. In both cases the amount of the total signal transferred will depend upon the ratio of the impedance across which the signal appears to the total impedance of the branch containing that impedance. Considering the branch supplying signals toV tube V1, it will be noted that the impedance of the condenser C1 will become innite at zero frequency, consequently no unidirectional components will be transferred to this tube, but with increasing frequency, the impedance of C1 will decrease and consequently at high frequency the total signal will be transferred by this tube. The signal transferred to tube V2 on the other hand, is taken from across the condenser C2, consequently, at zero frequency the entire signal will appear across Cz but with higher frequency the amount of signal will decrease. In a preferred form of the invention the ratio of the impedance R1 to the impedance of C1 may be made equal to the ratio of the impedance of R2 to the impedance of C2 for such desired frequencies. 'This may be done by making'the product R101 equal to the product RzCz. Under these circumstances the voltage to ground at the point connecting R2 and C2 together will be complementary to the voltage at the point connecting R1 and C1. Thus of the total Voltage appearing across the diagonal, the part appearing across the one impedance will be transferred by one tube, the part appearing across the other impedance will be transferred by the other tube, and as these two parts when added together give the total input signal, obviously each may be amplified by the same amount and then added to give an amplified total signal.

It will be noted that the blocking battery B1 may be used without the deleterious effects encountered in the use of such a battery in a conventional D. C. amplifier since the capacitance of the battery B1 to ground is in shunt with that of the condenser C2 and simply adds to it. It has been found that such an amplifier has a gain which may be independent of frequency over the video frequency range, that the output of the device will be similar in wave shape to the input even for transitory conditions and that there will be no phase distortion introduced.

A second stage similar to the one described may be coupled to the first stage as shown in Fig. 1. The corresponding elements of the two stages have been designated accordingly. Preferably the load resistance R3 is small as compared with R1 and R2 as is necessary for wide band video amplification.

In Fig. 2, there is illustrated another form of the device which comprises four stages in the A. C. amplifier circuit and only two stages in the D. C. amplifier circuit. These stages are substantially identical with the corresponding ones of the preceding figure and the parts are correspondingly designated. The use of a lesser number of stages in the D. C. amplifier branch than in the A. C. amplifier branch is made possible by tlie fact that the gain per stage obtainable in the conventional video signal amplifier is relatively low due to the fact that low impedances must be used to minimize the effect of the capacity to ground of the customary blocking condensers, whereas this restriction does not apply to the D. C. compensator branch. Consequently,

while it may be necessary to use, say four stages of A. C. amplification, as illustrated in Fig, 2, the same gain may be obtained in the D. C. compensator branch by the use of two stages as shown.

In Fig. 3, the gain vs. frequency characteristics are shown for the single and multi-stage amplifiers of Figs. 1 and 2. The solid line curves l and 2 are those of a single and multi-stage amplifier as in Fig. i, the curve i being the curve of the A, C. amplifier stagewhile the curve 2 is that of the D. C. compensator stage. It will be seen that the curve 2 shows rapidly decreasing gain until a cut-off point is reached at a relatively low frequency. This depicts in an exaggerated fashion the disadvantage of the D. C. amplifier as above mentioned, and is due largely to the filter R202, it having been pointed out above that the cut-off at relatively low frequency prevents amplification throughout any useful video signal range. In this case the cut-off is due to the condenser Cz, however, in a conventional conductively coupled D. C. amplifier, the capacity to ground of the blocking battery would bring about the same result but at a higher frequency. It will also be seen that the curve I and the curve 2 are complementary so that a resultant curve 3 is obtained, which curve indicates that substantially uniform over-all gain is obtained throughout the video signal range. Due to the various stray capacities in the amplifier it will have the high-frequency cut-off common to all amplifiers which may, however, be made well above the video range by proper design.

When the device of Fig. 2 is employed, the A. C. amplifier branch exhibits a curve such as shown in broken-line representation at li. It will be noted that this curve shows a reduction in gain over the range of lower frequencies as compared tothe curve I. The resultant curve 5 of curves 2 and l, exhibits a slight reduction in gain at the lower frequencies. Inasmuch as this reduction in gain occurs at frequencies in the video signal range which are seldom encountered, the reduction is of little importance. In fact, this reduction may, in some instances, be desirable since it may be desired to diminish certain undesired signals at the frequencies in question. It is obvious that by suitably adjusting the gain of the D. C. amplifier branch, the gain at zero frequency, which is due entirely to the D. C. amplifier, may be made equal to the gain of the A. C. amplifier at high frequencies where the D. C. amplifier is substantially inoperative, It will be seen that the slight gain reduction at low frequencies represented in curve 5 may be charged, at least in part, to the low frequency attenuation introduced by the coupling elements C3 R4. This effect may be reduced, if desired, to almost any desired point through the proper choice of the relative values of R3, R4 and C3, as related to the vacuum tube plate resistance, as well as by the values chosen for the elements R1, R2, C1 and Cz of the input network. It is apparent that the relative values of the elements in this input network determine the frequency at which the gains of the two amplifier branches are equal. The negative vlow-frequency gain of the A. C. amplifier as represented in the dotted curve i is intended to indicate that phase reversals, due for example to the reactive coupling elements between the tubes V1, may, at low frequencies, result in an A. C. amplifier output which is out of phase with the D. C. amplifier output. Thus, if at some low frequency the signal output of the A. C. amplifier is out of phase with the output of the D, C. amplifier, the resultant gain will be proportional to the arithmetic difference or algebraic sum of the several outputs. Methods of computing the resultant gain where the phase difference is other than 180 are, of course, well understood in the art. It is understood that the curves in Fig. 3 are merely illustrative, and that in practice the characteristics may vary widely, depending upon the characteristics desired.

It Will be understood, of course, that the invention is not limited to the specific forms herein disclosed but is capable of other forms of expression without departing from its scope.

I claim: j c 1,. `In a` signal amplifyingdevice, a source of input signals having frequency Vcomponents within av predetermined range including Vzero frequency compo`nents,'an impedancefhaving a plurality of current paths supplied with signals from said source of input signals, means for deriving from one yof said current, paths a signal having a predetermined frequency response, means for deriving from another of said current paths a second signal having a predetermined vfrequency response substantially complementary to the said predetermined response of said first -derived signal, one of said derived signa-ls including said zero frequency components, means for amplifying said rst derived signal, means for amplifying said second derived signal, an output circuit, and means for combining said ampliiied signals in said output circuit.

`2. In a signal amplifying device, a source of input signals having frequency vcomponents within a predetermined range including zero frequency components, an impedance network sup'- plied with signals from said source of input signals, said network having a plurality of current paths in shunt relation, at least two of said current paths comprising a plurality of dissimilar impedance elements in series relation, means for deriving from one of said impedance elements of one of said current paths a signal having a, predetermined frequency response, means for deriving from a dissimilar impedance element of another of said current paths a second signal having a predetermined frequency response sub stantially complementary to the said predetermined response of said first derived signal, one of said derived signals including said Zero fre-- quency components, means vfor amplifying said first zero frequency components, means for amplifying said first derived signal, means for arnplifying said second derived signal, an output circuit, and means for combining said amplified signals in said output circuit. y

3. In a signal amplifying device, a source of input signals having frequency components within a predetermined range `including zero frequency components, an impedance network supplied with signals from said source ofV input slignals, said network having a plurality of current paths in shunt relation, at least two of said current paths comprising a plurality of dissimilar impedance elements in. seriesI relation, the ratio of the impedances of one of said current paths being substantially equal to the ratio of the impedances of another of said current paths for all frequencies within said predetermined frequency range, means for deriving from one of ,said impedance elements of one of saidI current paths a signal having a predetermined frequency response, means for deriving from one of said impedance elements of another of said current paths a second signal having a predetermined frequency response substantially complementary to the said predetermined response of said rst derived signal, one of said derived signals including said zero frequency components, means for amplifying said rst derived signal, means for amplifying said second derived signal, an output circuit, yand means for combining said,l amplified signals in said output circuit.

4, In a signal amplifying device, a source of input signals havingfrequency components within a predetermined range including zero frequency components, anA impedance network supplied with signals from said source of input signails, said network having a plurality of current paths in shunt relation, at least two of said current paths each comprising a capacitive element andat least another impedance element, means for deriving from said capacitive element of one of said current paths a signal having a predetermined` frequency response, means for deriving from said other impedance element of another of said current paths a second signal having a predetermined frequency response substantially complementary to the said predetermined vrespense of said first derived signal, one of said derived' signals including said Zero frequency components, means for amplifying said first derived signal, means for amplifying said Vsecond derived signal, an output circuit, and means for combining said amplified signals in said output circuit. Y

5. In a signal amplifying device, a source of input signals having frequency components within a predetermined range including zero frequency components, an impedance network supplied with signals from said source of input4 sighals, said network having a plurality of current paths in shunt relation, at least two of said current paths each comprising a capacitive element and atleast another impedance element, the ratio of the impedances of one of said current patlisbeing substantially equal to the ratio of the impedances of another of said current paths for all frequencies within said predetermined frequency range, means for deriving from. said capacitive element of one of said current paths a signal having a predetermined frequency respdnsermeans for deriving from said other im-` pedancc element of another of Said current paths a second signal having a predetermined frequency response substantially complementary to the said predetermined response of said :'rst derived signal, one 'or said derived signals 'inducing said zerofrequency components, means for amplifying said first derived signaLrmeans for amplifying sai'd second derived signal, an output circuit, 'and means for combining said amplified signals in said output circuit.

6; In a signal amplifying device, a source of input signals having frequency components witha predetermined range including Zero frequency components, an impedancenetwork supplied with signalsfrom said source of input signals, means for deriving from said network a signial having a predetermined frequency response, means for deriving from said network a second signal having a predetermined frequency response substantially complementary to the said predetermined response of said first derived signal, one of said derived signals including said zero frequency components, means for amplifying said derived signal including said zero frequency components, means for amplifying said other derived Asignal comprising an amplifier having a plurality of stages, an output circuit, and means for combining said amplified signals in said output circuit.

` 7. In a signal amplifying device, a source of input signals having frequency components within ha predetermined range `including zero frequency components, an"`iinpedance network supplied with signals from 'said source of input sig-` nals, means for deriving from said network a signal having a predetermined frequency` respouse, means for deriving from said network a second signal having a predetermined frequency response substantially complementary to the saidV predetermined response of said iirs't derived sig-` nal, one of said derived signals including said zero frequency components, means for amplifying said derived signal including said zero frequency components, means for amplifying said other derived signal comprising an amplier having a plurality of stages, said amplifier having substantially uniform gain over the frequency range in which the derived signal comprises an appreciable portion of the said input signal, an output circuit, and means for combining said amplified signals in said output circuit.

8. In a signal amplifying system for amplifying signals from a source of signals having low and high frequency components, a plurality of channels including at least one amplifier in each channel, means in the input circuit of one of said amplifiers for providing a biasing potential, said means introducing inherent capacity to ground, a signal tranfer network between said source and said channels, constructed and arranged to prevent by-passing of the high frequency components by said capacity, means for deriving from the said network a signal containing higher frequency components and for supplying the said derived signal to one amplifier, the said last-named means having a certain transfer frequency-response characteristic, means for deriving from the Said network another signal containing the lower frequency components and for supplying the said other signal to the biased amplifier, the said second deriving mean having a transfer frequency respense characteristic subtantially complementary to the rst-mentioned transfer characteristic, the

two signal ranges being overlapping, and means for combining the two amplified derived signals.

9. In a signal amplifying system for amplifying signals from a source of signals having low l and high frequency components, a plurality of channelsincluding at least one amplifier in each channel, means in the input circuit of one of said amplifiers for providing a biasing potential, said means introducing inherent capacity to ground, a signal transfer network between said source and said channels, constructed and arranged to include said capacity as one of the elements of the network and thus prevent by-passing of the high frequency components by said capacity, means for deriving from the said network a signal containing higher frequency componentsy and for supplying the said derived signal to one amplifier, the said last-named means having a certain transfer frequency-response characteristie, means for deriving from the said network another signal containing the lower frequency components and for supplying the said other signal to the biased amplifier, the said second deriving means having a transfer frequency response characteristic substantially complementary to the first-mentioned transfer characteristic, the two signal ranges being overlapping, and means for combining the two amplified derived signals.

10. In a signal amplifying system for amplifying signals from a source of signals having low and high frequency components, a plurality of channels including at least one amplifier in each channel, means in the input circuit of one of said amplifiers for providing a biasing potential, said means introducing inherent capacity to ground, a signal transfer network between said source and said channels, comprising a plurality of impedance elements arranged to provide a plurality of signal paths and including said capacity as one of the elements of the network, thus preventing by-passing of the high frequency components by said capacity, means comprising one of said signal paths for deriving from the said network a signal containing higher frequency components and for supplying the said derived signal to one amplifier, the said lastnamed means having a certain transfer frequency-response characteristic, means comprising another of said paths for deriving from the said network another signal containing the lower frequency components and for supplying the said other signal to the biased amplier, the said second deriving means having a transfer frequency response characteristic substantially complementary to the first-mentioned transfer characf teristic, the two signal ranges being overlapping,

and means for combining the two amplified derived signals.

1l. In a signal amplifying system for amplifying signals from a source of signals having low and high frequency components, a plurality of channels including at least one amplifier in each channel, means in the input circuit of one of said ampliers for providing a biasing potential, said means introducing inherent capacity to ground, a signal transfer network between said source and said channels, constructed and arranged to prevent by-passing of the high frequency components by said capacity, said network comprising a plurality of current paths in shunt relation, at least two of said current paths comprising a plurality of dissimilar impedance elements in series relation, means for deriving from one of said paths a signal containing higher frequency components and for supplying the said derived signal to one amplifier, the said last-named means having a certain transfer frequency-response characteristic, means for deriving from the other of said paths another signal containing the lower frequency components and for supplying the said other signal to the biased amplifier, the said second deriving means having a transfer frequency-response characteristic substantially complementary to the first-mentioned transfer characteristic, the two signal ranges being overlapping, and means for combining the two amplified derived signals.

12. In a signal amplifying system for amplifying signals from a source of signals having low and high frequency components, a plurality of channels including at least one amplifier in each channel, means in the input circuit of one of said amplifiers for providing a biasing potential, said means introducing inherent capacity to ground, a signal transfer network between said source and said channels, constructed and arranged to prevent by-passing of the high frequency components by said capacity, said network comprising a plurality of current paths in shunt relation, at least two of said current paths comprising a plurality of dissimilar impedance elements in series relation, the ratio of the impedances of the elements of onepath being substantially equal to the ratio of the impedances of the elements of the other path for all frequencies within the signal range, means for deriving from one of said paths a signal containing higher frequency components and for supplying the said derived signal to one amplifier, the said last-named means having a certain transfer frequency-response characteristic, means for deriving from the other of said paths another signal containing the low-er frequency components and for supplying the said other signal to the biased amplifier, the said second deriving means having a transfer frequency-response characteristic substantially complementary to the first-mentioned transfer characteristic, the two signal ranges being overlapping, and means for combining the two amplified derived signals.

13. A signal amplifying device comprising a source of input signals having frequency components within a predetermined range including Zero frequency components, a first resistor and first capacitor serially connected in shunt with said signal source, a second capacitor and second resistor serially connected across said signal source, means for amplifying the signal Voltage across said second capacitor, said signal voltage comprising the lower frequencies and the Zero FRANK J. BINGLEY. 

